Swift 中与枚举相关的对象缺少 ObservableObject 和 @Published 包装器，从而阻止状态更改更新 UI

Question

我有一个 MainViewModel，它保存具有关联对象的枚举数组。但是，当我在 SwiftUI 视图中使用它时，变量会丢失其 @Published 包装器，并且 UI 不会更新或收到更改通知。如何保留变量的 @Published 状态？

这是我的代码：

// Enum with associated types
enum ViewType: Hashable, Identifiable {
    case .a(ViewModelA)
    case .b(ViewModelB)
    case .c(ViewModelC)
}

// classes used in associated types
class ViewModelA: ObservableObject {
    @Published var listIndex: Int = 1
    //some other properties
}

class ViewModelB: ObservableObject {
    @Published var name: String = "hello"
     //some other properties
}

class ViewModelC: ObservableObject {
    @Published var isOn: Bool = false
     //some other properties
}

// then I create an array in my mainViewModel
// to use in my SwiftUI view
class MainViewModel: ObservableObject {
    @Published var viewTypeArray: [ViewType] = [] // add items to it based on the backend response (assume I have 4 items)
}


// then I use the viewModel in my view
struct MyView: View {
    @ObservedObject viewModel: MainViewModel

    init(viewModel: MainViewModel) {
        self.viewModel = viewModel
    }

    var body: some View {
        ForEach(viewModel.viewTypeArray) { view in
            case .a(let viewModelA):
               // I display something
               // I loose the ObservableObject wrapper
               // then I lose the connection to @Published wrapper properties ex: `listIndex`
               // and no ui updates will trigger here
            case .b(let viewModelB):
               // I display something
               // I loose the ObservableObject wrapper
               // then I lose the connection to @Published properties ex: `name`
               // and no ui updates will trigger here
            case .c(let viewModelC):
               // I display something
               // I loose the ObservableObject wrapper
               // then I lose the connection to @Published properties ex: `isOn`
               // and no ui updates will trigger here
        }
    }
}

我尝试为每个子 ViewModel（例如 ViewModelA、ViewModelB）使用 ObservableObject 包装器来保持与视图的直接连接，但这不起作用。我想使用具有关联类型的枚举以及 @ObservableObject 和 @Published 包装器，以确保更改正确更新 SwiftUI 视图。

Answer 1

您可以使用包装器有选择地公开特定的

@Published

属性。

struct PropertyWrapper<T: ObservableObject, Content: View>: View {
    @ObservedObject private var value: T
    private var content: (T) -> Content

    init(value: T, @ViewBuilder content: @escaping (T) -> Content) {
        self.value = value
        self.content = content
    }

    var body: some View {
        content(value)
    }
}

然后按如下方式使用它：在

case .b

 ForEach(viewModel.viewTypeArray) { view in 
            switch view {
                case .a(let viewModelA):
                   // I display something
                   // I loose the ObservableObject wrapper
                   // then I lose the connection to @Published wrapper properties ex: `listIndex`
                   // and no ui updates will trigger here
                case .b(let viewModelB):
                   PropertyWrapper(value: viewModelB) { object in 
                     Text(object.name) // this should update the UI properly when `name` updates
                   }
                case .c(let viewModelC):
                   // I display something
                   // I loose the ObservableObject wrapper
                   // then I lose the connection to @Published properties ex: `isOn`
                   // and no ui updates will trigger here
            }
        }

我希望这能如预期那样进行。玩得开心。